Generally, as an example of a pressure adjusting device incorporated into a liquid discharge apparatus, a device that maintains a pressure of a meniscus of an ink jet head in a proper range is known. In such a pressure adjusting device, for example, a pressure of the liquid is adjusted by a combination of a volume change of air within a cylinder, for example, due to movement of a piston arranged within the cylinder and a switching operation of an opening and closing member that opens and closes a flow path of the liquid.
In such a device, the piston arranged within the cylinder is moved in an axial direction and an opening and closing valve and the like are driven to be opened and closed according to a moving position of the piston in the axial direction. Therefore, the moving position of the piston in the axial direction is accurately controlled when moving the piston in the axial direction by, for example, a pulse motor.
In addition, there is a fluid shutoff device including a stepping motor as a driving source and a shutoff valve that drives a valve body and performs opening and closing of a flow path by converting a rotational movement of the stepping motor into a linear movement. In the device, a magnetic reed switch is in a state of being turned ON and thereby an opening and closing state of the shutoff valve is detected as an electric signal.
In a case where the moving position of the piston in the axial direction is accurately controlled, it is necessary to accurately detect an origin point position of a rotation shaft of the pulse motor. Since there is a variation in sensitivity in the reed switch, the reed switch can be used for detecting opening and closing, but it is difficult to use the reed switch to accurately position a position of the shutoff valve. Therefore, as a unit that detects the origin point position of the rotation shaft of the pulse motor, it is difficult to use the magnetic reed switch.
In addition, as a unit that detects the origin point position of the rotation shaft of the pulse motor, it is also considered to use a mechanical switch in which two electrical contacts are arranged to be contactable and separable and which detect an electric signal by contact between the two electrical contacts. However, when the moving position of the piston within the cylinder is detected by the mechanical switch, it is necessary to use an electrical wiring structure for wiring signal lines and the like. Then, when the mechanical switch is arranged within the cylinder on a closed area side, it is necessary to seal the signal lines and the like, whereby the structure is complicated and increased in size. Thus, while it is desirable to use the mechanical switch in an area within the cylinder, which is not the closed area, since there is the pulse motor on a side which does not need to be sealed, a space-saving switch is required.